MiSTer FPGA Forum

Someone sent me this x86 core:
https://github.com/marmolejo/zet

We know ao486 core offers x86 instructions, but it does not run properly older games (even by reducing CPU MHz).

As it is already implemented in FPGA, would it be so difficult to port to Mister?

Thanks!!!

jordi wrote: ↑Fri Oct 02, 2020 10:32 am We know ao486 core offers x86 instructions, but it does not run properly older games (even by reducing CPU MHz).
As it is already implemented in FPGA, would it be so difficult to port to Mister?

Can't we just have an option to make ao486 even slower?

Newsdee wrote: ↑Fri Oct 02, 2020 12:06 pm

jordi wrote: ↑Fri Oct 02, 2020 10:32 am We know ao486 core offers x86 instructions, but it does not run properly older games (even by reducing CPU MHz).
As it is already implemented in FPGA, would it be so difficult to port to Mister?

Can't we just have an option to make ao486 even slower?

ao486 implements a 32 bit system (386-486). 8086 is a 16 bit cpu and it is much much slower than a 486, even if it runs at the same speed as the 8086, it will work different. Some programs or games made for 8086/8088 may still run on the 32 bit cpu, but a lot of them will fail to run properly. It is like two different systems that are somehow compatible (but not always).

Some games / programs may even require the 8088 at 4.7 Mhz and won't run well on the 8086, but as far as I know, the 8088 and 8086 are nearly identical, so we could have an option to choose and change the speed.

286 are still 16 bit, but they are very fast, so most software made for them will work well on ao486.

I see what you mean... there are a few lists of games that would run best on a 4.77Mhz XT (and why), such as this one:
http://nerdlypleasures.blogspot.com/201 ... d.html?m=1

A project to port Zet on Mister : https://github.com/RW-FPGA-devel-Team/zet_MiSTer

There is also this code... not sure how it compares to Zet, but it is more recent:
https://github.com/jamieiles/80x86

I use SLOWDOWN or MOSLO with great success for older titles (early 80s) like Castle Wolfenstein, Sopwith, Airborne Ranger and such.

From my side, I'd love to see a real 8088-XT 4-77Mhz with a turbo 8Mhz with the option of having a CGA and Hercule graphic card with why not the Tandy CGA like most of the PC at this era. There is one demo that none of the current emulators are capable to run perfectly, it is this demo
https://trixter.oldskool.org/2015/04/07 ... emulators/
I'd love to see it running on the Mister like it runs on a real XT-8088 @ 4.77mhz + CGA.

For slowdown programs I recommend cpuspd - it's a very recent utility, imo better than Mo'slo and the rest. Handles even 1982-83 games on my P4 2.4Ghz.

I would like to see an XT core, too. I grew up playing games on my grandparents' color IBM XT during many summers. It was definitely a unique experience compared to our 386 clone. Even the HDD seek sounds gave the experience a distinct flair.